-a kill all children processes -k unconditionally kill - nn specify which signal to send, in decimal, rather than the default sigterm which is 15. See the Technical Reference Manual or Programmer’s Manual for details of signals available, which generally follow U NIX conventions. The WAIT command The WAIT inbuilt command returns when the selected PID has terminated. It may be used to synchronise asynchronous commands. For example, suppose there is a background process called download running. We wish to report when the program has finished. A command to do this is: "wait download ! echo ^G^G^G >con:" & This command will suspend until the completion of download and then emit some beeps.
Using pipes A pipe is created by typing vertical bars | between two or more commands. The operating system starts each command asynchronously, connecting the output of eachcommand tothe inputof thenextviaan interprocess pipe. Ifthe lastcommand in the pipeline was run synchronously, the system blocks until it is complete. Standard input for every command in the pipeline, except the first, comes from thestandardoutputofthepreviouscommand. Standardoutputforeverycommand, except the last, goes onto standard input for the next. You can also pipe standard error using the ^ symbol, however this can not be done while also using the normal pipe.
Thecommandline pipesare verysimilar tothepipes providedbythe pipe memory resident driver under earlier single-tasking 1616/OS versions. The important dif- ference is that under multi-tasking, all the specified tasks are run simultaneously, whereas the pipe MRD ran them sequentially, connecting their input and output via temporary files. This temporary file kludge is still used by MS-DOS, which explains several pipe collapses in that system. Command line syntax 1616/OS command lines are getting quite complicated nowadays, so a review is in order. The command line in its entirety is interpreted by the exec system call, so all the following comments apply to that call.
The following characters have a special meaning on the command line: Page 60 User Tutorial Manual Multi Tasking